Recent years have seen increased high performance in electronic devices such as mobile information devices and information appliances following the development of digital technology. As such, there is an increasing demand for higher-capacity, reduced power consumption, such as reduction in writing power consumption, increased speed during writing and reading, extended operational life, or the like of nonvolatile memory elements. In response to such a demand, it is said that there is a limit on the miniaturization of existing flash memories using floating gates. On the other hand, a nonvolatile memory element (a variable resistance element) that uses a variable resistance material as a material of a memory unit can have a simple structure. Thus, further miniaturization, increase in speed, and reduction of power consumption are expected, and the research and development is advancing (e.g., see PTL 1).
Here, a variable resistance element refers to an element which has characteristics that the resistance state reversibly changes in response to application of a voltage pulse, and can store information in a nonvolatile manner by associating resistance states to correspond to information
More specifically, the variable resistance element has a simple structure which includes, between a first electrode layer and a second electrode layer, a variable resistance layer comprising a resistance change material. For example, in the case of a bipolar type variable resistance element, a resistance change phenomenon occurs in the variable resistance layer when voltage pulses having different polarities are applied between the first electrode layer and the second electrode layer (between the electrodes). Specifically, for example, when a negative voltage pulse is applied between the electrodes, the state of the variable resistance layer achieves a low resistance state. Conversely, when a positive voltage pulse is applied between the electrodes, the state of the variable resistance layer achieves a high resistance state. Such a variable resistance element can store two values, for example, by assigning “0” to one of a low resistance state and a high resistance state and assigning “1” to the other. The nonvolatile memory device using a variable resistance element is a memory device which makes use of a variable resistance layer that changes to at least two states, namely, a high resistance state and a low resistance state. The memory device performs, on each of the variable resistance elements, writing and reading of information according to the resistance state.
As a technique regarding a variable resistance element, for example, a variable resistance element in which two tantalum oxide layers having different oxygen content atomic percentages are stacked and used as a variable resistance layer is disclosed (see patent literature (PTL) 1, for example). Note that, after the manufacturing of the variable resistance element, a breakdown voltage is applied once in an initial stage, in order to allow the layer that include the two tantalum oxide layers, which have different oxygen content atomic percentages and are stacked, to function as a variable resistance layer. A voltage value of the breakdown voltage is, generally, a value larger than a voltage value of a voltage pulse which is applied in a normal operation to cause a change in a resistance state of the variable resistance layer.